The third generation partnership project (3GPP) and 3GPP2 are currently considering a long term evolution (LTE) of the universal mobile telecommunication system (UMTS) terrestrial radio access (UTRA). Currently, OFDMA is being considered for the downlink of the evolved UTRA.
In an OFDMA system, a plurality of orthogonal subcarriers is transmitted simultaneously. The subcarriers are divided into a plurality of localized subcarrier blocks, (also known as resource blocks). FIG. 1 illustrates two localized subcarrier blocks, each comprising four subcarriers, as an example. Each of the localized subcarrier blocks is defined as a set of several consecutive subcarriers. The localized subcarrier block is a basic scheduling unit for downlink transmissions in a conventional OFDMA system. Depending on a data rate or a buffer status, a Node-B assigns at least one localized subcarrier block for downlink transmission for a WTRU.
As with wideband code division multiple access (WCDMA) high speed downlink packet access (HSDPA), it is very difficult to implement inter-Node-B soft handover in the downlink OFDMA system since scheduling of downlink data transmission at different Node-Bs to support hybrid automatic repeat request (H-ARQ) operation is very difficult to coordinate. For soft handover, a new cell has to be selected by either the WTRU or the system. Therefore, it would be desirable to have a fast cell selection method for the OFDMA system.